In the past many individuals were overcome by smoke and toxic gases in their sleep as a result of household fires occurring during the night. Many other individuals lost their lives to structural fires because they did not receive warning of the fire until it had advanced to a stage from which they were unable to escape. Luckily, advances in smoke detection technology have allowed the development of reliable smoke detectors that can awaken occupants of a house, and alert occupants of a structure of the presence of a fire at a very early stage. Specifically, many modem smoke detectors provide an indication that a fire or hazardous condition may be present long before the amount of smoke could be detected by a person. The effectiveness of these devices is so great that they are now mandated in many states, and indeed in many countries, for installation in multiple-family dwellings, and even in single-family homes.
Recognizing that the early detection of a fire affords the occupants of a dwelling the best possible chance for survival, many manufacturers, and indeed many building codes, recommend the installation of multiple smoke detectors throughout a dwelling positioned in key locations. As a minimum, it is recommended that at least one smoke detector be included on each level of a multi-level dwelling, e.g., one located in the basement, one on the first floor, one on the second floor, and one in the attic. For multi-unit dwellings, it is recommended that at least one smoke detector be included in each dwelling unit, as well as one in each common area shared by the units, such as a hallway or fourier.
While the inclusion of multiple smoke detectors maximizes the opportunity for early detection of a fire regardless of its point of origin, occupants of a dwelling may not be able to hear the audible alarm from the smoke detector in a location remote from their position within the dwelling. For example, if a smoke detector in the basement of a dwelling were to detect the presence of smoke and were to sound its alarm, an occupant located in a second floor bedroom who is sound asleep with a radio playing may not be awakened until the condition has progressed to a point where one of the other smoke detectors begins to sense the smoke condition and sound its alarm. As a further example, occupants in one dwelling unit of a multi-family dwelling may be unaware that a smoke alarm in another remotely located dwelling unit has sensed the presence of a fire because of the amount of sound insulation between individual family dwelling units. In these situations, precious moments may be lost until the fire has progressed to a point that smoke detectors in proximity to the individuals have sensed the condition.
To overcome such a situation, many smoke detector manufacturers provide the capability for interconnecting the various smoke detectors located within a dwelling. In this way, once a single smoke detector has detected the presence of smoke anywhere within the dwelling, a signal is sent to all other smoke detectors so that they may sound their alarms as well. Utilizing such a system in the examples discussed above would result in all of the occupants being notified the moment that a single smoke detector began sounding its alarm. Through the interconnection of individual smoke detectors, the sleeping occupant on the second floor would be awakened by the smoke detector located on the second floor the moment that the smoke detector in the basement sensed the presence of smoke. Likewise, the occupants in a multi-family dwelling would be notified by the smoke detector in their particular dwelling once any smoke detector located throughout the multi-family dwelling sensed the presence of smoke. By constructing an interconnected multi-detector system, occupants are provided with their best chance for survival because they will be notified the moment that any detector distributed throughout their dwelling detects the presence of smoke.
To ensure that smoke detectors from multiple manufacturers can be utilized in such a distributed, interconnected smoke detector system, most detectors are compatible with a 3-wire interconnection. In this standard 3-wire interconnect, a first wire is utilized to supply voltage to the smoke detector, a second wire is used as the return, and a third wire provides the alarm signal indication to all of the smoke detectors. With this standard interconnect, any smoke detector that detects the presence of smoke generates an output voltage signal on the third wire of the interconnect to signal all other detectors to sound their smoke alarms. This alarm voltage is a DC level, which has been selected to be 12 volts DC. This DC level was chosen to ensure that noise induced on this signal wire would not inadvertently cause other smoke detectors coupled thereto to sound their smoke alarms. The number of smoke detectors that can be interconnected through such a system vary based on the design of the individual smoke detectors, and in particular based on the design of the driver circuit for this signal wire. These systems are so effective in increasing the amount of warning provided to occupants of dwellings that such an interconnection system is a standard feature of most new construction.
While smoke detectors have a long history of providing early warning to occupants of a dwelling of a hazardous condition, and have therefore been integrated within the building plan of new dwellings as evidenced by the interconnection systems available for these detectors, carbon monoxide detectors are a relatively new entrant into the personal hazardous condition market. However, with the advances in the detection of carbon monoxide, many people are recognizing the benefits that such detectors provide. This is especially true in northern climates where occupants rely on furnaces and fireplaces to heat their dwellings during the winter months. Indeed, since carbon monoxide is a clear, odorless gas, it is nearly impossible for a sleeping occupant to detect its presence within the dwelling without the use of a carbon monoxide detector.
As with the acceptance and incorporation of smoke detectors, it is now recommended that at least one carbon monoxide detector be included on each level of a multi-level dwelling, and in each living unit of a multi-family dwelling as well as in the common areas. Unfortunately, the same problems that plagued the distributed network of smoke detectors prior to the interconnection system described above also plagues the system of multiple distributed carbon monoxide detectors. That is, the sounding of a carbon monoxide alarm in a remote location within the dwelling may not be perceived by an occupant in another location within the dwelling. While a separate 3-wire interconnection system could be utilized specifically for the carbon monoxide detectors, such increases the amount of interconnection wiring required within a dwelling. This would significantly increase the cost of such a system, and therefore reduce its desirability. Additionally, many modern detectors are combination units providing both smoke and carbon monoxide detection and alarming capability. To increase the desirability of these combination detectors, they are being manufactured to be compatible with the current interconnection system in use for smoke detectors.
The Underwriters' Laboratory standard UL2034 requires that the carbon monoxide alarm's temporal pattern be four (4) short chirps followed by a 4.5 second pause before repeating the four (4) short chirps. The UL217 standard requires that the smoke alarm's temporal pattern be three (3) long beeps, followed by a 1.5 second pause, before repeating. Since these two distinct temporal patterns are to signify two completely separate hazardous conditions, the UL also requires that all units must sound the appropriate temporal pattern for the corresponding hazard that is detected. For example, if a smoke detector detects the presence of smoke and it is interconnected to a carbon monoxide alarm, the carbon monoxide alarm must either sound the smoke temporal pattern or alternatively remain silent. Conversely, if a carbon monoxide detector senses the presence of carbon monoxide and it is interconnected to a smoke alarm, the smoke alarm must sound the carbon monoxide alarm temporal pattern or alternatively remain silent.
Unfortunately, conventional smoke and carbon monoxide detectors, when interconnected via the standard 3-wire interconnect described above, respond to a single signal sent via the single I/O wire. If no hazard is detected, there is no signal present on this wire. When either hazard is present, be it smoke or carbon monoxide, the originating unit will send a voltage through the I/O wire. Sensing this signal, the interconnected units will then go into their individual alarm modes. Utilizing this standard DC voltage signaling protocol, conventional interconnected smoke and carbon monoxide detectors have no way of distinguishing whether the interconnected signal came from a smoke alarm or a carbon monoxide alarm. For example, if a smoke detector senses the presence of smoke, it sends out the interconnected signal to which all of the alarms connected thereto will respond, including the carbon monoxide detector, by sounding their corresponding alarm temporal pattern. This may result in a carbon monoxide alarm temporal pattern being sounded when the hazard is actually smoke, and vice versa. This is strictly prohibited by the UL.
There exists, therefore, a need in the art for an interconnection communication protocol which is capable of using the existing standard 3-wire interconnect for hazardous condition detectors, but which is able to discriminate between smoke and carbon monoxide hazardous conditions and which is compatible with existing detectors already deployed throughout the market.